Re: [PATCH 07/13] object-filter: common declarations for object filtering

> On Wed, 27 Sep 2017 13:09:42 -0400
> Jeff Hostetler <git@jeffhostetler.com> wrote:
> 
>> On 9/26/2017 6:39 PM, Jonathan Tan wrote:
>>> On Fri, 22 Sep 2017 20:30:11 +0000
>>> Jeff Hostetler <git@jeffhostetler.com> wrote:
>>>
>>>>    Makefile        |   1 +
>>>>    object-filter.c | 269 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>    object-filter.h | 173 ++++++++++++++++++++++++++++++++++++
>>>>    3 files changed, 443 insertions(+)
>>>>    create mode 100644 object-filter.c
>>>>    create mode 100644 object-filter.h
>>>
>>> I think these and list-objects-filter-* are multiple levels of
>>> indirection too many. Would a single file with a few implementations of
>>> filter_object_fn be sufficient?
>>
>> I did that in my first draft and I found it confusing.
>>
>> Each filter has 3 parts (some filter-specific data structures,
>> a filter callback routine, a driver to call the traverse code).
>> I found it easier to reason about each filter in isolation.
>> And it makes it easier to work on each independently and keep
>> their inclusion in separate commits.
> 
> I looked at object-filter.{c,h} a bit more. It seems that these files:
>   1) define a struct that contains all the options that we would want
>   2) supplies a way to populate this struct from code that uses parse-options
>   3) supplies a way to populate this struct from code that calculates
>      options by hand
>   4) supplies a way to populate this struct from "protocol" ("<key>" or
>      "<key> <value>" strings)
> 
> And the next commit takes the struct that object-filter.{c,h} produces
> and actually performs the traversal.
> 
> I think this can be significantly simplified, though. Would this work:
>   a) Define the object_filter_options struct, but make all fields
>      correspond to a single parameter each. Define
>      OBJECT_FILTER_OPTIONS_INIT to initialize everything to 0 except for
>      large_byte_limit to ULONG_MAX (so that we can detect if something
>      else is set to it).
>   b) Define one single OPT_PARSE_FILTER macro containing all the
>      parameters. We can use the non-callback macros here. That solves 2)
>      above.
>   c) Define a function that takes in (int *argc, char ***argv) that can
>      "massage" it to remove all filter-related arguments, storing them in
>      a object_filter_options struct. That solves 3) above. As discussed
>      in the API documentation, this means that argument lists of the form
>      "--unknown --known" (where "--unknown" takes an argument) are
>      processed differently, but then again, rev-list never supported them
>      anyway (it required "--unknown=<arg>").
>   d) Define a function that converts "<key>" into "--<key>" and "<key>
>      <value>" into "--<key>=<value>", and use the existing mechanism.
>      That solves 4) above.
> 
> This removes the need to maintain the lists of one-per-argument
> functions, including the parse_filter_* and opt_parse_filter_* functions
> declared in the header file. If we were to add a feature, we wouldn't
> need to change anything in the caller, and wouldn't need to hand-edit
> object_filter_hand_parse_arg() and object_filter_hand_parse_protocol().